meck:new fails if running in embedded mode and module not loaded

[bobergj]

When running erlang in embedded mode, meck:new fails if the (original) module exists, but isn't loaded.

How to repeat

1. Compile to following module:

$ erlc +debug_info test.erl

1. Start Erlang in embbedded mode and load all the modules needed by meck, and mock the test module:
   $ erl -mode embedded -pa meck/ebin/ -pa . -pa PATH_TO_ERL_INSTALL/lib//ebin/
   application:start(compiler).
   {ok, Modules} = application:get_key(compiler, modules).
   [ l(M) || M <- Modules ++ [meck, meck_mod, cover] ].
   4> meck:new(test).
   * exception exit: undef
   in function test:module_info/1
   called as test:module_info(compile)
   in call from meck_mod:compile_options/1
   in call from meck:backup_original/1
   in call from meck:init/1
   in call from gen_server:init_it/6
   in call from proc_lib:init_p_do_apply/3

Solution

Normally, in embedded mode, one doesn't meck a module that isn't. Thus, in practice the problem occurs when the module is first loaded and when running the sequence: meck:new(test), meck:unload(test), meck:new(test), since meck:unload doesn't load the original module, but rather relies on the code server auto-loading it.

• A potential fix would be to call code:ensure_loaded in meck:unload, and call code:load_file if that returns {error, embedded}. Since the original module doesn't have to exist, any errors from code:load_file would have to be ignored though.
• Perhaps meck:new should call code:ensure_loaded in the function backup_original, and not backup the original if the result is {error, embedded}.

[eproxus]

Closing this as 'not reproducible' for now. Haven't been able to produce a test case where this is repeatable. Please re-open with a pull-request and a test case if it's possible.